The regulation of interstitial fluid volume in the small bowel is governed by the interaction of transcapillary, lymphatic and transmucosal volume flows and forces. The interplay of these volume flows and forces is of utmost importance in assuring the prompt removal of absorbed nutrients and volume in the absorptive state yet limits excess accumulation of interstitial fluid due to capillary filtration in the nonabsorptive state. The overall objective of the studies outlined in this proposal is to more fully characterize the forces, membrane parameters, and flows which govern interstitial fluid volume regulation in the small bowel under various pathological (secretion, chronic hypertension, acute hypotension) and physiological (absorption, lumenal distension) conditions. Particular attention is given to studying the effect of the aforementioned conditions on a) capillary and interstitial forces and lymph flow, b) capillary permeability to small and large solutes, and c) physiochemical properties of the interstitium (e.g. macromolecule exclusion). From the information obtained in these studies we can build a comprehensive model of interstitial fluid volume regulation in the small bowel for various physiological and pathological conditions.